Coating apparatus including means to shape surface of coating bed



B. H. SHARP COATING APPARATUS INCLUDING MEANS TO SHAPE SURFACE OF COATING BED June 30, 1970 3 Sheets-Sheet 1 Filed June 26, 1967 INVENTOE B.H.SHAE F June 30, 1970 H, SHARP 3,517,647

COATING APPARATUS INCLUDING MEANS TO SHAPE SURFACE OF COATING BED Filed June 26, 1967 3 Sheets-Sheet 2 June 30, 1970 B. H. SHARP COATING APPARATUS INCLUDING MEANS TO SHAPE SURFACE OF COATING BED 3 Sheets-Sheet 3 Filed June 26, 1967 Ill United States Patent 3,517,647 COATING APPARATUS INCLUDING MEANS TO SHAPE SURFACE OF COATING BED Benny H. Sharp, Bethany, 0kla., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed June 26, 1967, Ser. No. 648,734

Int. Cl. Bc 11/14 US. Cl. 118-600 8 Claims ABSTRACT OF THE DISCLOSURE Tubular resistors having axial leads are heated and rolled over the top of a continuously-rising bed of powdered resin to pick up a coating of resinous material. Scrapers between adjacent resistors dress the surface of the bed to a contour matching the contour of the resistor in order to apply a uniform thickness of resin on all surfaces of the resistor. After passing through a curing oven to partially set the resin, the resistors are rolled over a long, contoured die that smooths and equally distributes the coating and squeezes air pockets out of the resin. The coating is then fully cured in another oven.

BACKGROUND OF THE INVENTION In the manufacture of deposited carbon resistors, a cylinder of insulating material is coated with a carbon deposit. Metallic caps are fastened to the ends of the cylinder in contact with the carbon, and axial leads are attached to the end caps. The carbon-coated cylinder is machined so as to develop a helical electrical path through the carbon coating to provide a predetermined electrical resistance between the metallic end caps. The cylinder and end caps are then covered with insulation to prevent direct electrical contact with the carbon coating of the cylinder or with the end caps.

In the copending application of B. H. Sharp, Ser. No. 629,072, filed on Apr. 7, 1967, it has been shown to be desirable to coat all of the cylindrical surfaces of a resistor with a uniform thickness of resinous insulating material that conforms to the shape of the resistor body formed by the carbon-coated cylinder and the metallic end caps.

Voids or air pockets in electrical insulation are usually undesirable since these voids or air pockets are points of possible failure of the insulation in the presence of a high electrical potential.

Therefore, it is an object of the present invention to apply a material to an article in a coating of controlled thickness and reduced porosity.

It is another object of the present invention to apply a coating of uniform thickness to an object having a nonuniform profile.

It is still another object of the present invention to distribute evenly a coating of material on the surface of an object.

A further object of the present invention is to remove voids and air pockets within the material coating of an object.

SUMMARY OF THE INVENTION In accordance with the present invention, an article is coated with material by advancing the heated article into contact with the top of a bed of finely-divided material,

and the thus coated article is rolled over a flat die having a contour similar to the profile of the article.

BRIEF DESCRIPTION OF THE DRAWINGS A complete understanding of the invention may be had by reference to the following detailed description when 3,517,647 Patented June 30, 1970 considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a side view of a machine for coating resistors according to the present invention;

FIG. 2 is a more detailed, enlarged view of the coating station of the machine of FIG. 1 but with several parts of the machine removed in order to show better the principle of operation;

FIG. 3 is a cross-sectional view of the coating station taken along line 3-3 of FIG. 2 and shows a resistor being rolled within the coating station;

FIG. 4 is a cross-sectional, enlarged view of the coating station taken along line 4-4 of FIG. 3 and shows in detail the scrapers dressing the top surface of the bed of material and also resistors rolling across the dressed bed of material;

FIG. 5, on the same sheet as FIG. 1, is a cross-sectional view taken along line 55 of FIG. 4 and shows a scraper dressing the top surface of the bed of material to conform to the shape of the profile of the resistor;

FIG. 6 is a more detailed enlarged view of the smoothing and rolling station of the machine of FIG. 1, with several parts removed for clarity; and

:FIG. 7 is a cross-sectional view of the smoothing station taken along line 7-7 of FIG. 6 showing a resistor in the smoothing die.

DETAILED DESCRIPTION Referring now to the drawings and more particularly to FIG. 1, there is shown a machine, according to the present invention, for applying a uniform coating of resinous material about a deposited carbon resistor. Resistors are supplied to the machine through a zigzag track 12 which delivers the resistors to a continuously-rotating metering wheel 14 that accepts resistors one at a time from the zigzag track 12 and delivers them to a pair of feed chains 16 and 17 that move in synchronism with the metering wheel 14.

As the feed chains carry resistors to the right in FIG. 1, these resistors first pass through an infra-red oven 20 which heats them to a temperature significantly above the melting temperature of the resin with which they are to be coated. The heated resistorsare then carried by the feed chains to a coating station 24 where the heated resistors are rolled across the top of a bed of powdered resinous material. Because the resistors are hot, they melt any particles of resin that touch them, and these melted particles adhere to the resistor body and immediately begin to cure or set. The resistors with melted resin thereon are then carried to another infra-red oven 30 Where further curing of the resin coating takes place; however, the resin is only partly cured as the resistors leave the oven 30, and the hot resin is still somewhat fluid.

Any voids or air pockets existing in an insulating coating on an electrical component are points of potential electrical failure and therefore must be eliminated. This is accomplished at a rolling or smoothing station 34 wherein the resistors with hot, partly-cured resin coatings are rolled over a steel die having a shape substantially conforming to the axial profile of the resistors, thereby smoothing and distributing the coating of resinous material that surrounds the resistor body. Once the coating has been smoothed and distributed about the resistor, the feed chains carry the resistor through yet another infra-red oven 40 in which the resinous coating is completely cured.

The two feed chains 16 and 17 are carried on six pairs of sprockets 35-1 through 35-6. Power is supplied to the feed chains by a motor and gear reducer 36 driving through a sprocket chain 37 to the sprockets 35-1. Another sprocket chain 38 provides drive power from the motor and gear reducer 36 to the smoothing station 3 34. To provide power to the coating station 24, a sprocket chain 39 is connected between the coating station and sprockets -3 that are driven by the feed chains 16 and 17.

COATING STATION Referring now to FIGS. 2, 3, 4, and 5, the coating station 24 is shown enlarged to illustrate details of its construction and operation. Any resistor 42 issuing from the oven 20 is carried by the feed chains 16 and 17 up the inclined ends of a pair of rails 44 and 45 which support the axial leads of the resistor, leaving the heated resistor body suspended between them. When a resistor reaches the top of the inclined ends of rails 44 and 45, a pair of rolling belts 46 and 47 press the leads of the resistor 42 tightly against the level surfaces of the rails 44 and 45. Movement of the rolling belts 46 and 47 in the direction shown by the arrows in FIGS. 2 and 4 causes the resistor 42 to roll clockwise as viewed in FIGS. 2 and 4, across the bed of powdered resinous material. The feed chain 16, the rail 44, and the rolling belt 46 have been omitted in FIG. 2, to show better the principle of operation of the coating station 24.

As mentioned in connection with FIG. 1, the coating station 24 is driven from sprockets 35-3 by the sprocket chain 39. This chain turns a driven sprocket 50 (FIG. 3) that is firmly connected to a shaft 53. Two toothed drive pulleys 51 and 52 are also firmly connected to the shaft 53 and drive the toothed rolling belts 46 and 47, thereby keeping precise synchronism between the movements of the feed chains 16 and 17 and the rolling belts 46 and 47.

A drive sprocket 55 also carried on the shaft 53 delivers driving power to another shaft 56 by means of a drive chain 57. A drive pulley 58 is firmly connected to the shaft 56 and rotates with it to move a toothed scraper belt 60 over the pulley 58 and an idler pulley 59 that is rotatably mounted on the shaft 53. Two other idler pulleys 61 are rotatably mounted on the shaft 56 and support the rolling belts 46 and 47. Only one of the idler pulleys 61 is shown in FIG. 2.

The scraper belt 60 carries a plurality of individual scrapers 62 that are fastened to its outer surface. These scrapers are interspersed between the resistors 42 and continuously dress or shape the top surface of the resinous coatingmaterial 66 ahead of each resistor. As best shown in FIG. 5 the axial profile of the resistor 42 is not a simple cylinder but has a cylindrical part 68 and two metallic end caps 70 to which the axial leads 72 are attached. Therefore, the edge of each scraper 62 has two projections 74 (best shown in FIG. 5) which dress the top surface of the resinous material 66 (material 66 is shown in FIGS. 4 and 5 and is omitted in FIGS. 2. and 3) into a shape that approximately matches the shape of the body of the resistors 42. Therefore, the coating that is applied to each resistor 42 is substantially uniform on each of its three cylindrical surfaces, and the shape of the coating approximately conforms to the shape of the resistor 42.

In order to supply sufficient material to the top surface of the dressed bed, a screw auger (FIGS. 2 and 3) is rotated by a motor 82 driving through a right-angle gear set 84 to deliver a continuously rising mass of material 66 to the scrapers 62 and the resistors 42. Auger 80 is contained within a guide tube 86 that is open at its bottom end to a material supply bin 88 for admitting powdered resinous material to the bottom of the auger 80. The rising resinous material propelled by the auger 80 is constrained in an upper chute 90 that shapes the bed into a long narrow profile below the resistors and the scrapers. Excess resinous material scraped from the bed by the scrapers 62 falls back into the supply bin 88 and is recirculated by the auger 80. An agitator 92 is driven by a gear-motor 94 and breaks up compacted lumps of the resinous material to provide only a finely-divided mass of material 66 to the scrapers and resistors.

Since the material 66 is continuously rising, it actually rises a small amount after the passage of each scraper but SMOOTHING STATION The smoothing station 34 is shown in greater detail in FIGS. 6 and 7 and comprises a steel die that is mounted on a base 101. The die 100 has a groove down its length that substantially conforms to the axial profile of the resistor 42. As hot resistors having a partly cured resin coating exit from the infra-red oven 30', they are introduced at the left-most end (FIG. 6) of the die 100 and to the inclined ends of two rails and 106. The feed chain 16 has been omitted in FIG. 6 for clarity,and part of the rail 105 and the die 100 have been shown removed, to illustrate better the operation of the smoothing station 34.

When the resistors 42 reach the level area of rails 105 and 106, they are engaged by two rolling belts 108 and and 109 which press on the axial leads of the resistor (FIG. 7) approximately midway between the rails 105 and 106 and the resistor body, thereby pressing the resistor agianst the die and rolling it clockwise (FIG. 6) to smooth the coating and squeeze out any voids or air pockets therein. Rolling belt 108 and its associated hardware have been omitted in FIG. 6, for clarity.

The rolling belts 108 and 109 are driven by the sprocket chain 38 (FIG. 7) which turns a drive sprocket that is firmly attached to a shaft 116. Two drive pulleys and 121 are also firmly attached to the shaft 116 and rotate with it, driving the belts 108 and 109 which are wrapped around them. The belts 108 and 109 are also wrapped around two idler pulleys 122 that are rotatably mounted on an idler shaft 123. Only one of the idler pulleys 122 has been shown in FIG. 6.

A pair of rigidly mounted pressure shoes 125 and 126 provide a firm backing for the rolling belts 108 and 109 which are kept tightly stretched across the bottom surfaces of the shoes 125 and 126. Four pressure rollers 130 are mounted in a movable carrier 131, and a spring 132 urges the carrier 131 downwardly to apply a load through the pressure rollers 130 to the top surface of the belts 108 and 109, thereby bending and tightening the belts.

Since the locations of the rails 105 and 106 are fixed and since the pressure shoes 125 and 126 can be held firmly fixed, the pressure under which the resistor 42 is rolled along the die 100 is determined by the stiffness and fiexural rigidity of the axial leads 72 of the resistor.

Therefore, the pressure with which resistors are rolled along the die 100 can be reduced by lowering the die more deeply into its mounting base 101. Conversely, the pressure with which the resistors are rolled can be increased by adding shims between the die 100 and the base 101 to raise the die 100'.

As a further alternative, the pressure shoes 125 and 126 can be mounted on eccentrics which can be rotated to raise or lower the pressure shoes 125 and 126 with respect to the rails 105 and 106 and the die 100.

The minimum length of the die 100 is determined substantially by the diameter (and thus the circumference) of the resistor 42 since the resistor should make at least one complete revolution along the die.

If printing or other indicia are to be put on the resistor bodies to indicate the value of resistance or to list some code number, it may be desirable to lengthen the die 100 and to use the smoothing station as a cooling station too, so that the resistors are cool when they exit from the right end (FIG. 6) of the die 100. When the partially cured resin is cooled, it temporarily solidifies and the resistors can be carried by hand or in large bins and can be stored for later printing and final curing.

In the alternative, a printing station can be inserted in the machine shown in FIG. 1 and can be located between the smoothing station 34 and the oven 40. A printer can then print resistance values and other indicia on the temporarily solidified resin coating and the coating and the marking material can be fully cured in the oven 40.

It is to be understood that the above-described arrangementsare simply illustrative of the application of the principles of this invention.

What is claimed is:

1. A machinne for applying a coating of material to the exterior surface of an article comprising:

means for generating a continuously-rising bed of the material in powder form;

means for dressing the shape of the top surface of the bed of material;

means for bringing the surface of the article into engaging relation with the top surface of the bed of material; means for smoothing the material adhering to the article evenly about the surface of the article; and

means for transporting articles to said means for bringing the article into engagement with the material and to said smoothing means.

2. A machine according to claim 1 wherein:

said generating means comprises a supply of material,

a driven elevator extending upwardly from said supply, and a return hopper to carry excess material to said supply.

3. A machine according to claim 1 wherein said dressing means comprises a plurality of scrapers; and

means for passing said scrapers across the upper surface of the material in synchronism with the transportation of the articles across the surface of the material, with a scraper position between each pair of articles.

4. A machine according to claim 1 wherein said smoothing means comprises a die having a profile across its width that conforms substantially with the axial profile of the article; and

means for rolling the coated article along the length of the die.

5. In an apparatus for coating articles with material:

means for generating a steadily rising mass of finelydivided material;

means for conveying articles across the top of the mass of material in contact therewith; and

means moving across the top of the mass of material and interspersed between adjacent conveying means for dressing the shape of the top of the mass of material.

6. An apparatus according to claim 5 wherein said generating means comprises:

a cylindrical }tube having two ends and having an axis oriented substantially in the vertical direction, with the lower end of said tube located in a supply of the material;

a screw with screw threads, said screw located within said tube,jand with one end of said screw in contact with the supply of material; and

means for rotating said screw in a direction to apply at raising force to any material in contact with the threads ofsaid screw.

7. An appaiatus according to claim 5 wherein said dressing meanscomprises a plurality of scrapers each positioned between two articles for scraping material from the top of the mass of material.

8. An apparatus according to claim 6 further comprising: Y

means for varying the speed of said rotating means for controlling the thickness of material coating the articles.

References Cited UNITED STATES PATENTS 2,771,047 11/1956 Zimmerman 22s-34 X 2,944,147 7/1960 Bolton 1l8- -637 X 2,986,114 5/1961 Fuchs et al. 118422 X 3,017,234 1/1962 Trimble et al. 3,053,215 9/1962 Guty 228-34 3,161,530 12/1964 'Strobel 117--18 3,291,630 12/1966 Deyle et al. 117-18 3,310,431 3/1967 Loose 117201 3,380,432 4/ 1968 Hester et a1 118- 600 X OTHER REFERENCES IBM Technical Disclosure Bulletin, Metal Coating Device With Dross Removal, C. H. Smith, Jr., vol. 8, No. 11 (April 1966), p. 1639.

MORRIS KAPLAN, Primary Examiner US. Cl. X.R. 

